time: doc: be more explicit about how the reference date works

[earthboundkid]

It seems like the reference date, being a novel idea in Go's time package, is a stumbling block for developers new to Go. I think it's worth adding a paragraph to the documentation for Parse and Format that is extremely explicit. Something along the lines of:

The following values are recognized:

month: 1 01 Jan January
day: 2 02 _2
hour: 3 03 15
minute: 4 04
second: 5 05 05.0 (etc.)
year: 6 06 2006
timezone: -07 -0700 -07:00 MST
day of week: Mon Monday
meridiem: pm PM

[ianlancetaylor]

CC @robpike

[gopherbot]

Change https://golang.org/cl/315795 mentions this issue: time: provide a concrete example for Format() and Parse()

[nogurenn]

@ianlancetaylor Hello. I'm not sure if I should ping here since I'm a first time contributor, but I've submitted a possible change in the documentation on gerrit.

EDIT: okay gopherbot is fast

[robpike]

The problem may be worth addressing; people do have trouble understanding the reference date (and that's on me).

I have an idea how to do this. Assigning to myself.